Invertebrates comprise 95% of all known species in the animal kingdom and include a vast diversity of animals from unicellular protozoans to the more complex echinoderms and protocordates. Many species of invertebrates are pests, especially the 750,000 known species of insects which compete with man for agricultural, forestal and animal products. Other invertebrate species act as vectors of diseases such as malaria and trypanosomiasis which affect more than one billion people. In contrast, some invertebrate species serve as food sources, such as mollusks and crustaceans, and are of commercial importance and, in some cases, commercially farmed. Thus, management of invertebrate species is important because of the impact of agriculture pests on the availability of food and other resources, the impact of vector born disease on human health, and the impact of disastrous outbreaks of disease in invertebrates of commercial importance.
One management strategy for control of invertebrate vectors of human or animal disease or agricultural pests involves the use of chemical pesticides. However, many pest species have never been successfully controlled with chemical pesticides. Moreover, some of the most effective chemical pesticides, like DDT, have been banned from use because of environmental and health concerns. Those pest species which have been successfully controlled or eradicated with chemical pesticides can become resistant to the chemical pesticides, necessitating the development of new chemical formulations. Although, chemical pesticides are still widely used, the problems of environmental contamination, risk to human health, and resistance represent serious drawbacks to relying solely on chemicals in the management of invertebrate pests.
The current management strategy of invertebrate pests involves integration of several different approaches including the use of biological control agents with or without the use of chemical pesticides. The biological control agents currently in use are either pathogens, parasites or predators (mostly larvivorous fish). A biological control agent used successfully is Bacillus thurigiensis which provides a toxin used to control growth of mosquitos, black flies, spruce bud worm, gypsy moth and lepidopterous pests. However, use of Bacillus thurigiensis and other infectious agents as pesticides represent less than 1% of the pesticide market. Biological pesticides have several drawbacks including higher cost, limited host range, low virulence, short shelf life, and difficulty in transportation. A better understanding of invertebrate immune defense mechanisms may contribute to optimal utilization of available biological pesticides and to the development of new biological control agents.
Management of commercially valuable invertebrate species is becoming more important as unfavorable conditions in aquacultures, commercial farms and the natural environment have led to an increase in fatal disease outbreaks. Unfavorable conditions include pollution of water and soils, crowded conditions that promote fighting and cannibalism and immobilization or capture of organisms which cause wounds. Commercial species of importance held in crowded conditions, like annelids, oysters, lobsters, penaeid shrimp, and soft-shelled crabs, can be decimated by infection with viruses, bacteria or fungi. Attempts to prevent these infections have not been described and an investigation of the immune response of these invertebrate species is essential to developing a strategy to prevent loss of these species both in nature and in the commercial farms.
Like vertebrate species, the immune system of invertebrates plays a central role in the resistance of the organisms to disease, however, little is known about invertebrate immune systems. It is known that invertebrates have both cellular and humoral components that can act in a coordinated way to provide protection from invading pathogens. Cellular responses mediated by hemocytes include phagocytosis, encapsulation, and various cytotoxic reactions such as release of lysozyme and activation of the prophenol oxidase system. These cellular responses are complimented by anti-bacterial action of lysozyme and anti-bacterial peptides known as the cecropins, attacins, diptericins and insect defensins. However, little is known about the early steps of the immune response as, for example, the transduction of foreign body invasion signals and subsequent initiation of early physiological defense responses. These early steps can be important in the eventual outcome of the infection, for example, an early immune response may prevent significant multiplication of a bacterial pathogen thereby preventing or delaying death of the host invertebrate.
Therefore it is an object of the present invention to identify steps in the invertebrate immune response, including early steps. It is also an object of the invention to develop compositions which can inhibit or stimulate the immune response in invertebrates. It is a further object of the invention to provide biopesticide compositions and methods of using these biopesticides to control growth of vectors of human disease and agricultural invertebrate pests. It is also an object of the invention to provide therapeutic compositions and methods of using therapeutic compositions to prevent fatal infections of invertebrate species of commercial value.